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HTTP/HTTPS Web Access does not work in v6.X.X firmware but works on v5.X.X in certain NMC2 configurations/environments

Issue

Upon upgrading to v6.X.X firmware on NMC2 devices, certain users have found that web interface access via HTTP or HTTPS no longer works. Though, access via other networking protocols such as Telnet, SSH, and FTP log-in work correctly so the problem appears isolated to web access.

Users accessing NMC2 over a WAN connection or VPN or other types of "remote" network subnet configurations

​Cause

APC has discovered a v6.X.X firmware issue affecting certain customers that prevents connectivity to the web interface of an NMC2 but other networking protocol access to the device (Telnet, SSH, FTP log-in, etc) is not affected. (While FTP log-in works properly, file transfers may not work properly.) It is most prevalent via WAN links or VPNs while local access to the same device, even from the same computer, works correctly. Customers that have WAN accelerators may not see the problem because the WAN accelerator compensates for the problem.

This problem has been investigated and a fix is being actively tested and validated.

Resolution

Long term, this issue has been resolved with AOS 6.4.0. Short term, users can temporarily (or permanently if it does not affect other applications in their environment) set their network Maximum Transmission Unit (MTU) on their computer to 1300 to see if web access begins to work, as a test. If it does, then this is likely the problem if everything except the web interface works.

Note: APC/Schneider Electric cannot be liable if changing the MTU setting on your PC/system causes other problems. Only experienced networking personnel should attempt this and proceed with caution and at your own risk in changing the MTU value whether temporarily or permanently.

If changing the MTU is not an option long term (as all HTTP/HTTPS access may be affected on the particular computer and run slowly or not work properly for other applications), the only workaround available at this point on the NMC2 side is to downgrade to v5.X.X for your application, if available. More information on downgrading is available in knowledge base article ID FA167693.

If changing this value does not show a change, then standard troubleshooting steps should be verified such as verifying general networking connectivity, proxy settings, IP address, firewall, etc.. Please contact APC technical support @ apc.com/support for assistance in verifying these items.